Electrical control apparatus



Feb. 15, 1938. w. A. TOLSON 2,108,152

ELECTRICAL CONTROL APARATUS Filed June 26, 1934 2 Sheets-Shet 1 men voz TA GE sup z Y CIRCUIT SUPPLY fi 10 l scnss/v GRIDS VERTICAL DEFLECTING' CIRCUIT HOHIZONTHL DEF'LECTM! ll INVEN'T'OR VViZZim fLToL son Feb. 15, 1938. w. A. TOLSON 2,108,152

ELECTR I CAL CONTROL APPARATU S WiZZiamA.Tolson Patented Feb. 15, 1938 UNITED STATES ELECTRICAL CONTROL APPARATUS William A. Tolson, Westmont, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application June 26, 1934, Serial No. 732,415

4 Claims.

My invention relates to electrical control apparatus and more particularly to methods of and means for maintaining synchronous operation in television systems and the like.

In television systems utilizing a cathode-ray receiver tube it is the general practice to synchronize the scanning at the transmitter with the scanning at the receiver by transmitting a horizontal synchronizing impulse at the end of each scanning line and a vertical synchronizing or framing impulse at the end of each picture frame. At the receiver, the synchronizing impulses are separated from the picture signals and impressed upon deflecting circuits which supply 15 the desired saw-tooth voltage or current waves to the deflecting devices of the cathode-ray tube.

In order that the two groups of synchronizing impulses shall control the proper deflecting circuit, they are separated from each other at the 20 receiver by means of filter circuits. To facilitate this separation of synchronizing impulses it has been found desirable to give the horizontal synchronizing impulses a different wave shape than the framing impulses, as disclosed in application 25 Serial No. 565,953, filed September 30, 1931, in the name of R. D. Kell, and assigned to the same assignee as this application.

In systems of the above described type, it has been the general practice to make each deflecting 30 circuit at the receiver a generator of saw-tooth Wave impulses. Such generators include an oscillator, such as a relaxation oscillator or a dynatron, which is adjusted to oscillate at a frequency slightly lower than the frequency of the syn- 35 chronizing impulses. By so adjusting the sawtooth Wave generator, the synchronizing impulses hold the generator in step therewith whereby the scanning at the receiver is synchronous with that at the transmitter.

40 The use of saw-tooth Wave generators which oscillate to produce deflecting waves whether synchronizing signals are being received or not has been fairly satisfactory, but such circuits involve the disadvantage that the oscillator of the 45 generator must be adjusted to oscillate at approximately the frequency of the synchronizing impulses.

An object of my invention is to provide an improved deflecting circuit for television receivers which does not have the above mentioned disadvantage.

More specifically, an object of my invention is to provide a deflecting circuit which supplies saw- 55 tooth waves of voltage or current which are completely under the control of the received synchronizing impulses.

A further object of my invention is to provide a deflecting circuit which is completely under the control of the received synchronizing im- 5 pulses but which is more responsive to the synchronizing impulses than to noise signals.

In practicing my invention the horizontal and vertical synchronizing signals are transmitted on the same carrier wave as described in the aboveidentified Kell application. At the receiver, the synchronizing signals are impressed upon deflecting circuits which produce a saw-tooth voltage or current wave only in response to the reception of a synchronizing signal.

In order to make the deflecting circuits at the receiver more sensitive to synchronizing impulsesthan to noise signals, I preferably include in each deflecting circuit an impulse amplifier comprising a blocking oscillator circuit, the oscillator tube being so biased that it will oscillate through only one oscillating cycle in response to the reception of a synchronizing impulse. The resulting impulse appearing in the output circuit of the impulse amplifier is then impressed upon the 5 wave-shaping portion of the deflecting circuit. Since the impulse amplifier or blocking oscillator cannot oscillate of its own accord, it is not pulled into step with the synchronizing impulses but, instead, it is directly driven by them.

Other objects, features and advantages of my invention will appear from the following description taken in connection with the accompanying drawings, in which Figure 1 is a circuit diagram of a preferred embodiment of my invention, and

Fig. 2 is a set of curves which are referred to in explaining the operation of the circuit shown in Fig. 1.

Referring to Fig. 1, a preferred embodiment 40 of my invention includes a radio receiver l in which the transmitted carrier wave is demodulated to obtain the picture signals and the horizontal and vertical synchronizing impulses. The picture signals and the synchronizing impulses are amplified in an amplifier 3 and impressed through a coupling condenser 5 upon the control grid 1 of a cathode-ray receiver tube 9.

The receiver tube 9 comprises an evacuated envelope i0 having an electron gun therein consisting of a cathode H, a screen grid l3 and a first anode 55. A second anode H, which consists of a metallic coating upon the inner surface of the envelope I0, is provided to accelerate the electrons projected from the electron gun and to aid in focusing them to the desired small point on a fluorescent screen at the end of the tube.

For obtaining horizontal deflection of the electron beam, electrostatic deflecting plates l9 are mounted inside the envelope Ill. The vertical deflection of the electron beam is obtained by means of external deflecting coils 2|.

The signal output of the amplifier 3 is impressed upon the input circuit of an electric discharge tube 23 which serves to separate the synchronizing impulses from the picture signals. The tube 23 includes a cathode 25, a control grid 21 and a plate 28. The grid 21 is connected to the cathode 25 through resistors and 3| and through a biasing battery 33 which supplies a small positive voltage to the control grid.

The synchronizing impulses are separated from the picture signals because of the fact that, having been transmitted in the manner described in the above-mentioned Kell application, they are more negative than the picture signals when applied to the control grid of the separating tube 23. In the output circuit of the separating tube 23, the horizontal synchronizing impulses are supplied through a condenser 35 and through a coupling condenser 37 to a blocking oscillator 39 in the horizontal deflecting circuit. The vertical synchronizing impulses are supplied through the condenser 35 and through an inductance coil M to a blocking oscillator 43 in the vertical deflecting circuit. This separating circuit is described and claimed in my copending application Serial No. 717,715, filed March 28, 1934, and assigned to the same assignee as this application.

Referring to the horizontal deflecting circuit, it includes a blocking oscillator or driver tube 45, an impulse tube 4'1, an amplifier tube 49 and a power output tube 5!. The blocking oscillator tube 45 may be of the screen grid type including a cathode 53, a control grid 55, a screen grid 51, a suppressor grid 59 and an anode 6|. The control grid 55 is connected through a grid leak resister 63 and through a biasing battery 65 to ground and through ground to the cathode 53. The grid circuit of the oscillator 39 also includes a grid condenser 61, the secondary 69 of a transformer H and a coupling resistor 13, the grid condenser, secondary and resistor being connected in series.

The anode BI is connected through the primary 15 of the transformer H to a suitable source of positive potential. The screen grid 51 is supplied with positive potential in accordance with ordinary practice, while the suppressor grid 59 is connected to the cathode 53.

The bias voltage applied to the controlgrid 55 by the biasing battery 65 is such that the oscillator 39 will not oscillate unless a voltage impulse is applied to the circuit from an external source and, when such an impulse is applied to the circuit, will oscillate through only one cycle and then stop. In the usual sense, therefore, the device 39 is not an oscillator since it will not oscillate continuously of its own accord. However, for lack of a more descriptive term, it will be referred to in the specification and claims as a blocking oscillator.

The action of the blocking oscillator is substantially as follows:

Assuming that potential has just been applied to the anode 68, the plate current begins to increase thus inducing a voltage through the transformer H into the grid circuit. The coupling between the plate and grid circuits is such that,

as the plate current increases, the control grid 55 is made more positive. The resulting positive potential on the control grid 55 causes a flow of grid current which charges the grid condenser 61 in a direction such that it tends to make the control grid 55 negative.

As the plate current reaches a maximum and approaches its saturation value, its rate of increase becomes less thus inducing less positive Voltage on the control grid whereby the plate current is caused to decrease in value. This reverses the direction of the induced voltage in the grid circuit whereby the control grid 55 is made so negative that the tube is biased beyond cutoff.

During the flow of grid current, the grid condenser 61 has been charged suificiently to hold the tube 45 biased beyond the cut-off point in the absence of any other voltage in the grid circuit. Therefore, until the charge has leaked off the condenser 61 through the grid leak resistor 63, the control grid 55 has a high negative bias thereon. Because of the biasing battery 65, however, even after the charge has leaked ofi the grid condenser 61, the tube is still biased beyond cut-off and the blocking oscillator will remain inactive until a voltage impulse from an external source causes the above described cycle of operation to start again. In the circuit illustrated, this external voltage impulse is the horizontal synchronizing impulse, and it is applied to the oscillator circuit through the coupling resistor 13.

The operation of the blocking oscillator as a driver tube will be more clearly understood by referring to Fig. 2, which indicates wave shape and phase relation but not relative magnitude. In this figure, the horizontal synchronizing impulse which appears across the coupling resistor 13 is represented by the curve 11, while the resulting voltage appearing in the grid circuit of the blocking oscillator 39 is represented by the curve [9. Attention is called to the fact that the voltage in the grid circuit is in the form of a highly damped oscillation.

Referring to the curves, it will be seen that at the time t1 the voltage on the control grid 55 of the driver tube 45 is that supplied by the fixed bias battery 65 and is below the cut-off point of the driver tube. At the time t2, the grid potential of the driver tube 45 has been raised by the incoming synchronizing impulse to the cutoff point, at which point plate current begins to flow and the cycle of operation is begun as shown. This cycle of operation is a typical blocking oscillator cycle such as described above, except that at the time is, when the charge has leaked off the grid condenser 61, the cycle does not repeat but, instead, the circuit is maintained in an inactive or static condition because of the fixed bias on the control grid 55. The time from t2 to ix may be referred to as the active period of the oscillator. The cycle of operation is not repeated again until the next horizontal synchronizing impulse occurs.

Attention also is called to the fact that the driver tube 45 is so adjusted that, with the fixed grid bias removed, it will oscillate to produce positive voltage peaks which have a smaller time interval between them than do the synchronizing impulses. That is, the interval between t2 and is (Fig. 2) is less than the interval between the horizontal synchronizing impulses 19. The reason for this adjustment is that it permits all the charge to leak off the grid condenser 61 and so return the driver tube 45 to its original state before the next synchronizing impulse occurs. This prevents the action of the driver tube, during the reception of one synchronizing impulse, from being influenced by a preceding synchronizing impulse.

It is evident from an inspection of Fig. 2 that so long as the charge is leaking off the grid condenser 61, noise signals must have an amplitude great enough to overcome the negative bias applied by the condenser 67 before they can cause the driver tube to produce a synchronizing impulse in its grid circuit. For this reason, my improved deflecting circuit is comparatively insensitive to noise signals during the greater part of the interval between synchronizing impulses.

A further advantage in the use of the driver tube 15 is that its output is substantially independent of variations in the amplitude of incoming synchronizing impulses. Also, the tube 45 is a very efiicient amplifier of the incoming impulses.

From the above description it will be understood that a positive voltage impulse appears in the grid circuit of the driver tube 45 as a horizontal synchronizing impulse each time a horizontal synchronizing impulse is received by the radio receiver i. If no synchronizing signals are being received, the entire deflecting circuit including the oscillator is in an inactive or static condition.

The above-mentioned positive impulses are impressed upon the impulse tube 41 through a coupling condenser 8i for producing a saw-tooth voltage wave. The circuit for producing such a voltage wave includes a condenser 83 in the plate circuit of the'impulse tube 41 so connected that it is charged through a variable plate resistor by energy supplied by a direct current supply 81. Each time a positive impulse is impressed upon the grid of the impulse tube 41, the condenser 83 is discharged through the plate circuit of the impulse tube. The resulting saw-tooth voltage wave is amplified by the amplifier tube 49 and impressed upon the input circuit of the power tube 5| through a coupling circuit which includes an inductance coil 89 and a blocking condenser 9!.

The inductance coil 89 is of such value that it resonates with the grid-cathode capacity of the power tube 5! at the high frequency end of the band of frequencies to be amplified. In some cases, additional capacity should be connected between the grid of the tube 5| and ground, as indicated at 93, in order to obtain resonance at the desired frequency. The tuned coupling circuit performs two functions, one being to increase the response of the amplifier at the higher frequencies and the other being to cut off the highest frequencies for a purpose which will be described later.

The amplified saw-tooth voltage wave is impressed through a coupling condenser upon the primary of an auto-transformer 91. This voltage wave appears at a much higher voltage across the terminals of the transformer secondary and is impressed upon the deflecting plates l9 through blocking condensers 99.

In order to prevent defocusing of the cathode beam during deflection, it is desirable to vary the voltage on the deflecting plates l9 about the second anode potential. This result is obtained by connecting a high resistance potentiometer llli across the deflecting plates l9 and by connecting the second anode i! to the mid-point of the potentiometer.

It was found that the leakage inductance of the transformer 91 resonated with its distributed capacity at a high frequency and that this resonance of the transformer introduced undesirable transients into the deflecting circuit. This difiiculty was overcome by making the leakage inductance a minimum whereby the resonant frequency was made higher than any frequency that must be transmitted to obtain a good saw-tooth voltage wave. Shock excitation of the transformer resonant circuit was then prevented by cutting off the high frequency components of the deflecting wave at a frequency below the resonant point of the transformer, this being accomplished by the above-described tuned coupling circuit.

Referring. now to the vertical deflecting circuit, it includes the blocking oscillator 43 comprising a vacuum tube ms which is biased by means of a biasing battery H35 beyond the cut-01f point, the same as the oscillator tube 45 in the horizontal deflecting circuit. The tube N13 has been illustrated as a three-element tube, but it should be understood that various types of tubes may be employed either in the horizontal block ing oscillator or in the vertical blocking oscillator. The oscillator 43 includes a grid condenser Hil a grid leak resistor l 09 and a feed-back transformer Hi, all of which perform the functions described in connection with the horizontal blocking oscillator 39.

The vertical synchronizing impulses are impressed upon the grid circuit of the oscillator 43 through a coupling resistor H3 which is included in the grid circuit in series with the secondary of the transformer Hi. Preferably, the resistor H3 is shunted by a condenser H5 for by-passing any horizontal synchronizing impulse component which may not be filtered out by the inductance coil 4 i.

The positive voltage impulses which appear in the grid circuit of the driver tube its in response to the reception of vertical synchronizing im pulses are impressed through a coupling condenser i l! upon an impulse tube 5 E9. The output circuit of the impulse tube H9 includes a condenser l2! having a variable resistor I23 connected in series therewith for supplying a voltage impulse wave containing a saw-tooth component. This voltage Wave apears across the inductance coil I25 in the plate circuit of a power tube I2! and is impressed across the deflecting coils 2! to produce a saw-tooth wave of current there through. The resistor 29, to which one terminal of the deflecting coils is connected, is provided for the purpose of adjusting the direct current component through the deflecting coils to center the electron beam on. the fluorescent screen.

Referring now to the voltage supplies for the deflecting circuits and for the cathode-ray tube, all the voltages for the tubes are supplied from the low voltage supply Bl across which a voltage divider i3! is connected. All the plates of the vacuum tubes are connected to the positive terminal of the Voltage divider Hit. The screen grids of the screen grid tubes are connected to a point of lower potential on the voltage divider I31 as indicated. The screen grid l3 of the cathoderay tube is connected to a point of still lower potential on the voltage divider Hi.

The cathode II of the cathode-ray tube is con nected to a point on the voltage divider l3| near its negative end and grounded, while the control electrode 1 of the cathode-ray tube is connected to the negative end of the voltage divider B! through a resistor I33 for maintaining it at the proper negative potential with respect to the cathode H.

The higher voltages for the anodes of the cathode-ray tube are provided by a high voltage supply I35 having a voltage divider I31 connected thereacross. The negative end of the voltage divider I3! is connected through ground to the cathode ll of the cathode-ray tube. The second anode I1 is connected to the positive end of the voltage divider 531, while the first anode I5 is connected to a point of lower potential on said voltage divider.

If the blocking oscillator or driver tubes 45 and I03 are omitted from the deflecting circuits and amplifiers substituted therefor the system, though entirely operative, is shorn of certain advantages. By impressing the synchronizing impulses directly, or through amplifiers, upon the impulse tubes 41 and H9, the deflecting circuits will be somewhat more sensitive to noise signals which is objectionable providing the ratio of synchronizing voltage to noise voltage is not high.

In either embodiment of my invention, the impulse tubes 4'! and H9 are preferably biased close to or beyond cut-ofi. They may be biased beyond cut-oii by inserting a biasing battery (not shown) in the grid circuit. In the particular circuit illustrated, which is the preferred one, the tubes 41 and [iii are biased close to cut-oif by means of the flow of grid current in the coupling condenser-grid resistor combination.

Referring to the tube 41 as an example, a positive voltage impulse from the blocking oscillator 39 causes a flow of grid current to charge the condenser 8 I Between positive voltage impulses, the condenser discharges through the grid resistor 8 to maintain the grid of the tube negatively biased. If the blocking oscillator is replaced by an amplifier (two resistance coupled vacuum tubes, for example) the biasing circuit shown is especially desirable as the bias on the impulse tube increases with increase in signal strength whereby an automatic volume action is obtained.

Whether the deflecting circuits are used with or without the driver tubes, the action of a deflecting circuit is to reshape a synchronizing impulse of the character generated in a transmitter such as described in the above-mentioned Kell application into either a saw-tooth voltage wave or a saw-tooth current wave for deflecting an electron beam. The advantage of such a directly driven deflecting circuit is that there is no possibility of the scanning at the television receiver getting out of synchronism with the scanning at the television transmitter.

The portion of the circuit comprising the tuned coupling circuit for the power tube the transformer 97, the potentiometer l0! and the rest of the electrostatic deflecting circuit is described and claimed in my copending application Serial No. 737,163, filed July 27, 1934, and assigned to the same assignee as this application.

From the foregoing description it will be understood that various modifications may be made in my invention without departing from the spirit and scope thereof and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claims.

I claim as my invention:

1. In combination, a generator of electrical impulses comprising an electric discharge tube having a control grid and having plate and grid circuits coupled to make said tube tend to oscillate, means for applying a biasing potential to said grid such that said generator can oscillate to produce an electrical impulse only in response to receiving a potential on said grid from a source external to said oscillator, and a non-oscillatory generator of electrical impulses having a saw-tooth wave shape, said first generator being coupled directly to said second generator.

2. In combination, an amplifier tube having an input circuit and an output circuit, a series circuit including a condenser and a resistor connected in series, means for charging said condenser through said resistor, means for applying voltage from said series circuit to said input circuit, an electric discharge tube having principal electrodes and a control electrode, said principal electrodes being connected across said condenser, means including an electric discharge tube which is normally biased beyond cut-off for generating a highly damped oscillation in response to, and only in response to, the reception of a'voltage impulse and means for impressing at least a portion of said damped oscillation upon said control electrode.

3. In combination, non-oscillatory means for producing an electrical impulse having a sawtooth wave shape in response to the reception of a voltage pulse of predetermined magnitude, a blocking oscillator comprising an electric discharge tube biased beyond cut-off whereby an oscillation of short duration is produced each time a voltage impulse is impressed thereon, and means for applying at least a portion of said oscillation to said first means.

14. In combination, means for producing electrical impulses having a saw-tooth wave shape in response to the reception of voltage pulses of predetermined magnitude, said means being characterized in that it is not self-oscillatory, a blocking oscillator comprising an electric discharge tube having a control grid and having input and output circuits so inductively coupled that the tube tends to oscillate, said input circuit including a grid condenser and a grid leak resistor, said input and output circuits having such damping and said grid condenser and grid resistor having such values that in the absence of a fixed bias on said control grid the oscillator repeats a cycle of operation, each cycle consisting of a damped sine wave and a period of rest and having a duration less than the interval between said voltage pulses, means for applying a fixed bias to said grid such that said tube is biased beyond cut-01f whereby it can oscillate only upon the reception of one of said voltage impulses, and means for impressing at least a portion of said damped sine wave upon said first means.

WILLIAM A. TOLSON. 

